Actually, I didn't draw the underside line for the bottom of the neck, so I think you're seeing his mane. Yeah, I tend to draw BIG eyes, LOL! Once I make the main outline then everything else around it, it comes out a bit big.
By jowl, do you mean the underside of his head, between the chin and the jaw? Or did you mean the main, half-circle shaped jaw bone? I think I get what you mean.
For the shading, I look at a 3-D horse model - it really helps for what dark spots should be where. I haven't taken any art lessons, and this particular sketch was done freehand.
Thanks guys! Now I know what to fix next time!